Airplanes, boats, hovercraft, and other vehicles are propelled by accelerating a fluid to generate a thrust. The thrust produces a force that drives the vehicle in a direction opposite to the direction of the thrust. Conventional propulsion systems generally include propellers and turbines.
Propeller propulsion systems are widely used in connection with airplanes and boats. Propellers, however, are relatively inefficient because a significant percentage of the fluid is directed radially outward away from the desired direction of the thrust. Accordingly, propellers waste energy on fluid that only marginally increases the thrust output. Propellers are also subject to cavitating when operating in water which further reduces their efficiency. Another problem with propellers is that they are dangerous, resulting in severe injury or even death to persons or animals that come into contact with the propellers as they rotate. Lastly, propellers are exceptionally noisy, creating a public nuisance around airports.
Turbines are widely used to propel airplanes. Turbines, however, have limited applications because they are expensive and noisy. Turbines also do not operate in high-density fluids such as water. In light of the problems with propellers and turbines, it would be desirable to develop a propulsion system that is efficient, safe, quiet, and widely applicable to land, sea, and air vehicles.
One alternate propulsion system is a rotating cylinder. Previous inventions regarding rapidly rotating cylinders have generally focused on using cylinders in a fluid flux to generate lift according to the Magnus effect. Although such applications of a rapidly rotating cylinder are useful for lift, they do not address using a rapidly rotating cylinder to generate a thrust force in a static fluid.
Rotating cylinders have not been widely accepted as a fluid propulsion system to date. When a cylinder is rotated in a fluid, the friction between the cylinder and the fluid causes a portion of the fluid to be entrained in a layer about the cylinder. Conventional propulsion systems using rotating cylinders do not generate sufficient thrust without exceeding the physical dimensions of a given vehicle such as wing span (airplanes) or beam (boat and cars). Thus, to date, rotating cylinders have been impractical to use on full-size applications of planes, boats, hovercraft, and other vehicles.
One propulsion system using rotating cylinders is shown in U.S. Pat. No. 2,985,406, issued to H. W. Bump, which discloses two rotatable cylinders that act as the lift and propulsion means for an aircraft. The cylinders are positioned substantially parallel to each other and rotated towards each other so that the air flows around the cylinders and converges at the rear of the cylinders. The air is initially entrained from the space between the cylinders and directed around the outside of the cylinders. If left unobstructed, the direction of the accelerated fluid in the space between the cylinders would generally be opposite to the desired direction of maximum thrust. To appropriately direct the accelerated fluid, Bump places a deflector at the rear portion of the cylinders that separates the accelerated air from the cylinders, and angles it 90.degree. to direct it in the desired direction.
Rotating cylinder propulsion systems have many advantages compared to propellers and turbines. First, such systems are relatively safe compared to propellers because they do not have any blades and they create a layer of inviscid fluid flow next to the cylinder that generally prevents objects from actually contacting the surface of the cylinders. Rotating cylinders are also exceptionally quiet, and equally applicable to operating in air or water. Therefore, it would be desirable to develop an efficient and flexible propulsion system using rapidly rotating cylinders, or another type of continuous dynamic surface such as a rapidly moving belt, for accelerating and directing a static fluid.